1. Field of the Invention
This invention relates to a legged walking robot, particularly a biped walking robot.
2. Description of the Related Art
A legged walking robot, specifically a biped walking robot, is taught in, for example, Japanese Laid-open Patent Application No. Hei. 11(1999)-48170. In this prior art, upon discriminating that the robot is in danger of falling down, a movable arm is brought into contact with the floor (or ground) to prevent falling.
Legged walking robots, particularly biped walking robots, are structurally unstable. They are apt to losing their balance and toppling during walking when subjected to an unexpected external force, such as upon collision with an obstacle, or when encountering unexpected irregularities in the floor surface. When a robot falls forward, it generally comes down on its knee joint regions. These regions of the robot receiving the impact are likely to be damaged. The floor or other structure struck by the robot may also be damaged.
On the other hand, when a robot falls sideways or backwards and regions around the knee joint regions have come in contact with the floor (kneeling state), an attempt to make the robot stand by controlled driving will be futile if the robot""s center of gravity is located forward of the knee joint regions in contact with the floor. The same problem always arises when trying to make the robot stand from a kneeling attitude, even when it did not fall down but was deliberately controlled into a kneeling attitude to carry out a particular job.
This will be better understood from FIG. 19. FIG. 19A shows the robot in a kneeling attitude, i.e., with its feet, knee joint regions, and movable arms in contact with the floor. The attitude shown is that resulting from controlling to drive robot joints for restoring the robot to the standing attitude. Specifically, the movable arms are extended to maximum length, the knee joints are bent to the limit, and the thigh links and shank (crus) links are driven to the permissible minimum angle therebetween. The robot""s center of gravity XG is forward of the point at which the knee joint regions come into contact with floor, hereinafter referred to as knee floor contact point Xknee.
The knee floor contact point Xknee and the center of gravity XG are represented as distances along the x axis from the origin of a coordinate system whose origin is the floor contact point directly under an ankle joint and whose x axis lies in the direction of robot advance.
Where the robot mass is m and acceleration of gravity is g, a force of F=mg is exerted downward at the center of gravity XG of the robot, and floor reaction forces f1, f2 and f3 occur at the points where the feet, knee joint regions and movable arms make contact with the floor, thereby maintaining equilibrium (F=f1+f2+f3).
In order to stand the robot from this state, its joints have to be driven to move the body rearward. However, the robot""s center of gravity lies forward of the knee floor contact point (Xknee less than XG). Therefore, as shown in FIG. 19B, the downward force F at the robot""s center of gravity XG operates as a force causing the robot to fall forward.
More specifically, the robot becomes incapable of holding its attitude because the moment produced around Xknee prevents production of a negative floor reaction force (downward force) at the feet. In this state, the body cannot be controlled by joint driving and, instead, the legs rotate forward around the knees joints. This raises the feet off the floor and makes it impossible to restore the robot to a standing attitude.
A first object of the present invention is therefore to provide a legged walking robot, more specifically, a biped walking robot, that can be easily stood up from an attitude with its knee joint regions in contact with the floor, i.e., from a kneeling attitude.
As previously stated, when a legged walking robot, particularly a biped walking robot, falls forward, it generally comes down on its knee joint regions. The regions of the robot receiving the impact are likely to be damaged. The floor or other structure struck by the robot may also be damaged.
A second object of the present invention is therefore to provide a legged walking robot, more specifically, a biped walking robot, that when coming into knee-first contact with the floor can absorb the impact of the contact to protect its knee joint regions and the floor from damage.
For realizing these objects, the present invention provides in a first aspect a legged walking robot having at least a body and a plurality of articulated legs each connected to the body through a hip joint and having a knee joint and an ankle joint; wherein the improvement comprises: a landing means is mounted at a position adjacent to the knee joint which is brought into contact with a floor when coming into knee-first contact with the floor such that the knee joint is to be positioned at a location forward of the center of gravity of the robot in a direction of robot advance.
For realizing these objects, the present invention provides in a second aspect a legged walking robot having at least a body and a plurality of articulated legs each connected to the body through a hip joint and having a knee joint and an ankle joint wherein the improvement comprises: a shock absorbing means is mounted at a position adjacent to the knee joint which is brought into contact with a floor to absorb impact occurring from the contact with the floor when coming into knee-first contact with the floor.